Issues with ozone depletion have resulted in an R22 phase out that begins in the year 2010. This has driven the majority of commercial refrigeration installations toward R125 and R143A blend refrigerants having the required zero Ozone Depletion Potential (ODP). On the negative side, these refrigerants have lower system efficiencies than R22 and also have high Global Warming Potential (GWP).
Refrigerant subcooling has been used to raise the system efficiencies. Mechanically coupled subcooling, in particular, has been used for larger refrigeration and air conditioning systems employing the same or similar refrigerants for both the main and the subcooling circuits. The efficiency increase, however, has not been accompanied by any meaningful reduction in GWP.
Certain blended refrigerants are available having zero ODP and low GWP are available for air conditioning application, but have not seen use in commercial refrigeration installations because they have performance issues that make them less practical than alternative refrigerants, i.e. very high discharge pressures, which means large refrigerant pipes with limited pressure ratings cannot be applied to these refrigerants, or significant temperature glide, which means there can be more than one temperature in a refrigerant system at a given pressure. Both present engineering and design problems for service contractors in commercial installations with long pipe runs.
Table 1 below is a summary chart of the characteristics of the refrigerants mentioned above. The data in this table is readily available as common knowledge in commercial refrigeration.
TABLE 1DischargePressure at 120 F.RefrigerantGWPApplicationCondensingR404A3859Refrigeration310 psigR5073925Refrigeration322 psigR410A1997Air Conditioning418 psigR407C1674Air Conditioning266-300 psigR221780Refrigeration & Air260 psigConditioning
The commercial refrigeration systems with subcooling have typically been large, field assembled systems and they have often been problematic from an operational standpoint. The combination of high installed capital cost, high maintenance cost, and limited contractor experience leads refrigerant subcooling technology toward use only on refrigeration systems of 25 Hp, or larger, compressor size. This size limitation works against current public sentiment for higher system efficiency in all size applications without addressing the concurrent sentiment for lower environmental impact.